It is radioactive. You don't need fission or fusion for an isotope to be unstable and decay giving off radiation. All long-term unstable isotopes give off either alpha--a helium nucleus (heavier than Fe 56 generally)-- or beta--an electron (lighter than Fe 56)-- particle when they decay. Decay chains will continue until the isotope created becomes stable. You start with one atom, you end with one atom, only the element the atom is changes with the decay process.
Fission requires a neutron source to cause the isotope (atom) to split into two new isotopes (atoms)--unlike radioactive decay where you get a single new isotope-- or fusion where you smash two atoms together to form a single new atom.